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| - Diffuse Layer Properties of Thiol-Modified Gold Electrodes Probed byDirect Force Measurements
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| - The diffuse layer properties of modified gold electrodes under potentiostatic control have been determined by directforce measurements. These measurements have been performed with a colloidal probe consisting of a silica particleattached to the cantilever of an atomic force microscope. The gold electrodes were modified by self-assembledmonolayers (SAMs) of different thickness. Additionally, the terminating functional groups of the monolayer have beenvaried. The interaction force profiles have been fit to the full solutions of the nonlinear Poisson−Boltzmann equation.An accurate quantitative description of the force profiles has been obtained by taking charge regulation between thesurfaces into account. The diffuse layer potentials obtained from these fits were studied in dependence of the potentialapplied to the gold electrode. The capacitance of the SAM and the potential of zero charge (pzc) have been determinedfor various SAMs of different thickness and surface termination. The values obtained by our direct force measurementsare in agreement with the ones reported by classical electrochemical techniques. The capacitance of the SAM dependsprimarily on the thickness of the monolayer and its crystalline structure. Pronounced differences in the pzc for thedifferent functional groups have been found. These changes are related to the dipole moment of the functional groupterminating the SAM. Our data are in agreement with ion adsorption, but this effect seems to be less pronounced thanfor bare gold electrodes.
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